feat: Add stores for copilotMessages and copilotThreads (#11603)

- Set up stores for copilotThreads and copilotMessages.
- Add support for upsert messages to the copilotMessages store on
receiving ActionCable events.
- Implement support for the upsert option.

app/javascript/dashboard/helper/actionCable.js

@@ -33,6 +33,7 @@ class ActionCableConnector extends BaseActionCableConnector {
       'conversation.read': this.onConversationRead,
       'conversation.updated': this.onConversationUpdated,
       'account.cache_invalidated': this.onCacheInvalidate,
+      'copilot.message.created': this.onCopilotMessageCreated,
     };
   }
 
@@ -189,6 +190,10 @@ class ActionCableConnector extends BaseActionCableConnector {
     this.app.$store.dispatch('notifications/updateNotification', data);
   };
 
+  onCopilotMessageCreated = data => {
+    this.app.$store.dispatch('copilotMessages/upsert', data);
+  };
+
   onCacheInvalidate = data => {
     const keys = data.cache_keys;
     this.app.$store.dispatch('labels/revalidate', { newKey: keys.label });